The field of art to which this invention pertains is the solid-bed adsorptive separation of impurities from an aqueous saccharide solution. More specifically the invention relates to a process for separating certain impurities from an aqueous saccharide solution which process employs a sorbent comprising a long chain alkyl cationic surfactant deposited on a hydrophobic microporous polymeric support which selectively adsorbs the impurities from the solution. The invention also relates to the sorbent composition itself.
Sugar producing processes, whether they are based on sugar beets, sugar cane or hydrolyzed corn starch as sources of sugar, all have in common an intermediate process stream comprising an aqueous saccharide solution which contains various impurities. The exact nature and amount of such impurities will vary from process to process, but generally they comprise phenolics, dextrans, amino nitrogen containing compounds and various other color bodies. The phenolics may account for up to 90% of the color bodies. It is necessary that these impurities be removed in order to obtain a high quality sugar product fit for human consumption.
A long used method for removing impurities from sugar solutions employs particles of activated carbon. The sugar solution or syrup is forced through a bed of such particles maintained in a vessel such as a column. Unfortunately, there are many disadvantages to such use of activated carbon, including (1) the high cost and complexity of regeneration which must be carried out by unloading the carbon from the vessel in which it is used, placing it in a kiln in which the impurities are burned off and reloading the carbon into the vessel; (2) the loss of sugar which adheres to the activated carbon and is destroyed during regeneration; (3) the slow rates obtainable (1-3 bed volumes/hour) of the sugar solutions through the activated carbon; and (4) certain limitations of activated carbon to deal with a high color loading (greater than 2,000 ICU) in the aqueous sugar feedstream.
More recently, various processes have been developed which employ ion exchange resins for the purification of aqueous sugar solutions. The process of U.S. Pat. No. 3,982,956 to Schoenrock et al treates impure sugar juice that has already undergone a two-stage carbonation, by first passing it through a cation exchange resin and then through an ion exchanger having a tertiary amine functionality, and regenerating the anion exchanger with an ammonium hydroxide solution. The process of Belgium Pat. No. 846,174 decolorizes sugar solutions first by precipitation of impurities with calcium hydroxide and phosphoric acid, followed by passing the solution over cation and anion ion exchange resins which contain 5% of a macroreticular absorbing porous resin or polymer. Japanese Patent Publication JP No. 77059722 (Abstract No. 453564) discloses decolorizing a sugar solution by contacting it with a conjugate fiber of one component made from an ion exchange polymer reinforced by a second component comprising a polymer such as poly-2-olefin. The publication "Cane Sugar Decolorization By Ion Exchange Resins", Sugar Industrial Technology, 1982, Vol. 41, discusses the use of quaternary ion exchange resins to remove the color bodies from sugar syrup passed through the resin at the rate of about 3 bed volumes/hour, and the use of NaCl brine for regeneration of the resin.
U.S. Pat. No. 4,196,017 to Melville et al teaches a method for reducing color impurities in sugar syrups by a multi-step process. First, a bleach is added to the syrup. Second, a cationic surfactant, such as a long hydrocarbon chain quaternary ammonium compound, is added. Third, a defecant such as calcium chloride is added. Finally, the solids are filtered out of the syrup and a purified sugar syrup is obtained.
The article "Adsorption of Organic Compounds from Water with Porous Poly(tetrafluorethylene)", Anal. Chem., 1984, 56, 764-768 discusses the use of Teflon in column chromatography for the adsorption of varius solutes from water.
The present invention relates to the removal of impurities from an aqueous saccharide solution, but, in a manner not known to the prior art, employs a long hydrocarbon chain cationic surfactant deposited on a porous hydrophobic polymeric support, and, in contrast to the methods of the prior art, the present invention is capable of purifying aqueous saccharide solutions having very high levels of impurities, and, for a given volume of sorbent, is capable of a very high throughput of solution.